FIG. 1 shows a structure of a traditional oxide semiconductor thin film transistor (oxide thin film transistor). As shown in FIG. 1, the traditional oxide thin film transistor comprises, sequentially from bottom up, a base substrate 10, a gate electrode 11, a gate insulating layer 12, an active layer 13, an etch stop layer 14, source/drain electrodes 15, a protective layer 16 and a pixel electrode 17.
FIGS. 2 (a) to 2 (g) show a traditional method of manufacturing the oxide thin film transistor. As shown in FIG. 2 (a), the traditional manufacturing method comprises firstly forming the gate electrode 11 on the base substrate 10; as shown in FIG. 2 (b), forming the gate insulating layer 12, which covers the substrate 10 and the gate electrode 11; as shown in FIG. 2 (c), forming the active layer 13 on the gate insulating layer 12 corresponding to the gate electrode 11, the active layer 13 being made of an oxide semiconductor material (e.g., indium gallium zinc oxide (IGZO)); as shown in FIG. 2 (d), forming the etch stop layer 14 on the active layer 13; as shown in FIG. 2 (e), forming the source/drain electrodes 15 on the etch stop layer 14; as shown in FIG. 2 (f), then forming the protective layer 16 to cover the source/drain electrodes 15, the etch stop layer 14 and the gate insulating layer 12; and as shown in FIG. 2 (g), finally forming the pixel electrode 17 on the source/drain electrode 15 and the protective layer 16.
Compared with the process of manufacturing the amorphous silicon (a-Si) thin film transistor, the process of manufacturing the oxide thin film transistor has an additional process for forming the etch stop layer (i.e., the step shown in FIG. 2 (d)). The characteristics of the oxide thin film have greatly affected by the interfacial characteristics, especially the thin film deposition process of the etch stop layer, which requires for example the silicon oxide thin film manufactured in the process for forming the etch stop layer to maintain a low content of hydrogen, generally lower than 6%; in contrast, in the amorphous silicon thin film transistor, the silicon nitride thin film has a hydrogen content of about 20%. On one hand, the purpose of the process for forming the etch stop layer is to prevent the etchant from corroding the active layer when performing etching process on the source/drain electrodes; on the other hand, the etch stop layer is usually formed by the silicon oxide materials, and in order to maintain a low hydrogen content of the silicon oxide thin film, the plasma enhanced chemical vapor deposition (PECVD) method is usually adopted to deposit the silicon oxide thin film. When the PECVD method is used, the hydrogen ions generated by silane decomposition are prone to react with In, Zn, O in the metal oxides (e.g., IGZO) in the active layer, affecting the characteristics of the IGZO thin film. Accordingly, the currently adopted solution is to lower the deposition temperature to about 200□, but it may increase the hydrogen content in the deposited silicon oxide thin film in the condition that the reaction gas has a constant flow rate, and thus the stability of the thin film is deteriorated and the deposition rate of the thin film is reduced.